The present invention relates to a method for fuel supply to a diesel engine, and, more particularly, relates to a novel method for fuel supply to a diesel engine which is fitted with a soot catcher of a per se well known sort, which is adapted to purge the soot catcher. The present invention also relates to apparatus for performing the above mentioned fuel supply method.
Nowadays, it is common and conventional to provide a soot catcher to the exhaust system of a diesel engine. Such a soot catcher catches and accumulates carbon particles and other solid particles present in the exhaust gases of the diesel engine, and prevents their escape to the atmosphere. Since it is becoming more and more realized nowadays that such soot particles such as carbon particles may present a significant health hazard to the public, the provision of such a soot catcher is very important from the environmental and public health point of view.
Such a soot catcher normally has a filter like structure for catching the soot particles, and naturally this filter structure inevitably tends to become clogged up, over a long period of use of the soot catcher, with an accumulation of soot particles, chiefly carbon particles. When this happens, not only does the efficiency of the soot catcher for purifying the exhaust gases of the diesel engine of soot particles drop drastically, but also the resistance of the soot catcher to the flow therethrough of exhaust gases increases, which deteriorates the actual operation of the diesel engine, causing its breathing efficiency to drop, which causes a loss of engine power. This has presented a serious problem with regard to such a soot catcher; either it has been necessary to regularly remove the soot catcher in order to clean it, which is dirty, expensive, and troublesome; or some system has had to be provided for cleaning or purging the soot catcher in situ, without removing it from the engine.
It is possible to purge such a soot catcher by burning out the combustible soot particles such as carbon particles which are clogging the filter structure of the soot catcher by increasing the temperature of the exhaust gases passing through the soot catcher above the ignition temperature of said combustible soot particles.
During normal operation of the diesel engine, when the load on the diesel engine rises to a high load level wherein the excess air ratio in the exhaust gases becomes small, it is quite possible for the temperature of the exhaust gases passing through the filter structure of the soot catcher to spontaneously rise above the ignition temperature of the soot particles clogging the soot catcher, without the provision of any special means for raising the temperature of said exhaust gases. In this case, purging of the soot catcher as described above may spontaneously occur, by burning out said soot particles lodged therein as a clogging accumulation. However, this spontaneous self purging process cannot be relied upon. Diesel engines, especially in automotive vehicles, are only irregularly operated in high load conditions; and when an automotive vehicle is being operated in urban traffic it is quite unusual for the diesel engine thereof to be operated in the high load operational region. Thus such spontaneous self purging of a soot catcher might not occur in time to purge the soot catcher before its clogging had unacceptably deteriorated the functioning of the diesel engine to which it was fitted. Therefore it is necessary to practice some particular special and reliable method for raising the temperature of the exhaust gases of the diesel engine to a temperature higher than the ignition temperature of the soot particles which are becoming lodged in the soot catcher thereof, in order reliably to purge said soot catcher whenever it becomes clogged.
A first such prior art method for raising the temperature of the exhaust gases of a diesel engine to a temperature higher than the ignition temperature of the soot particles which are becoming lodged in the soot catcher thereof in order to purge said soot catcher has been to delay the timing of fuel injection to the diesel engine.
However, this first prior art purging method has suffered from the disadvantage that the temperature of the exhaust gases of the diesel engine can only be so raised when the engine is operating in a certain range of operational conditions; in other engine operational conditions the temperature of the exhaust gases does not rise up sufficiently to combust the soot particles in the particle catcher, even when fuel injection timing is delayed. Further, delaying the timing instant of fuel injection may hamper the operability of the diesel engine, and the drivability of a vehicle to which it is fitted. Accordingly the first purging method is not of very good applicability.
A second such prior art method for raising the temperature of the exhaust gases of a diesel engine to a temperature higher than the ignition temperature of the soot particles which are becoming lodged in the soot catcher thereof in order to purge said soot catcher has been to reduce the amount of excess air which is supplied to the combustion chambers of the diesel engine, by limiting the air intake of the engine.
However, this second prior art purging method has also suffered from the disadvantage that the temperature of the exhaust gases of the diesel engine can only be so raised when the engine is operating in a certain range of operational conditions; in other engine operational conditions the temperature of the exhaust gases does not rise up sufficiently to combust the soot particles in the particle catcher, even when the air intake amount of the engine is limited. Further, reducing the air intake amount of the engine also reduces the volume of the exhaust gases which are passed through the soot catcher, which means that the efficiency of heat transfer to the filter structure of the soot catcher from the exhaust gases is deteriorated. Also the amount of heat energy transferred by this reduced amount of exhaust gas is correspondingly reduced. Accordingly this second purging method is also not of very good applicability.
A third such prior art method for raising the temperature of the exhaust gases of a diesel engine to a temperature higher than the ignition temperature of the soot particles which are becoming lodged in the soot catcher thereof in order to purge said soot catcher has been to provide a separate heater, such as an oil burner or other heating device, for heating the exhaust gas up.
However, this third prior art soot catcher purging method has suffered from disadvantages related to safety and durability. In practice this solution cannot practically be used for a diesel engine for use in an automotive vehicle.